Search area off the coast of Pangkalan Bun, Borneo, is a graveyard of battleships

A metal structure detected in the Java Sea that proved to be a false lead in the hunt for the wreckage of AirAsia flight QZ8501 was "possibly a ship which sank" during the Second World War, Indonesian search-and-rescue chief SB Supriyadi said.

Although he said it was unlikely to have been a warship, the search area off the coast of Pangkalan Bun, Borneo, is a graveyard of sunken ships from when allied forces were defeated by the Japanese during the war.

In the Battle of the Java Sea on 27 February 1942, the Allied navies, known as the American-British-Dutch-Australian (ABDA) Command, led by Rear Admiral Karl Doorman, lost the fight to protect the Dutch East Indies (now known as Indonesia) against the Japanese.

It was a major naval battle in the Pacific campaign, and the largest ship engagement since the Battle of Jutland in 1916. The ABDA lost 2,300 of their men and five warships – two light cruisers and three destroyers – compared to the Japanese navy, which only lost one destroyer and 36 men.

Other smaller naval conflicts, including the significant Battle of Sunda Strait involving Australian and US forces, later took place between 28 February and 1 March. Three allied warships were damaged and 1,037 people killed. One Japanese cruiser was damaged and four troop ships were sunk.

In November 2013 Indonesian researchers discovered the German submarine U-168 that was torpedoed off Java during the war. It is believed to have succeeded in sinking several allied vessels before itself being torpedoed by a Dutch submarine in 1944.

Seventeen human skeletons were found on the wreck as well as dinner plates bearing swastikas, batteries, binoculars, and a bottle of hair oil.

"This is an extraordinary find that will certainly provide useful information about what took place in the Java Sea during World War II," Bambang Budi Utomo, head of research at the National Archaeology Centre that found the vessel, said at the time.

Meanwhile, the search for Airbus A320 has moved underwater with specialised acoustic detective devices now being deployed in a bid to locate the plane and its black box recorders.

Thirty bodies have so far been recovered from the sea, and four people have been identified so far – Grayson Herbert Linaksita, Kevin Alexander Soetjipto, AirAsia stewardess Khairunnisa Haidar Fauzie, and Hayati Lutfiah Hamid. All four victims were Indonesian.

It is believed the flight got into difficulty after trying to climb to 36,000ft to avoid bad weather.

"Its speed had dropped by about 200km/hr, which was not enough speed to sustain flight," Geoffrey Thomas, the editor-in-chief for FlightRatings.com, told Channel NewsAsia.

The Dutch East Indies was one of the most valuable European colonies in the Dutch Empire, having been formed from the nationalised colonies of the Dutch East India Company in 1800.

The Japanese dismantled much of the Dutch colonial state and economy. But following their surrender in August 1945, Indonesian nationalists declared their independence, which they fought and gained during the Indonesia National Revolution. The Netherlands then formally recognised Indonesian sovereignty in 1949.